Power amplifier and radio communication device using the amplifier

ABSTRACT

A power amplifier includes amplifier elements to amplify input signals of different frequencies. The amplifier also includes a power supply circuit that includes a common power supply path including an end connected to a power supply input terminal connected to a DC power supply. The amplifier further includes individual power supply paths each including an end connected to the other end of the common power supply path, and the other end connected to the main electrode of a corresponding one of the amplifier elements. The individual power supply paths have different impedances.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2003-147917, filed May 26, 2003,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power amplifier mainly for ahigh-frequency band, and more particularly to a power amplifier thatselectively amplifies a plurality of input signals of differentfrequencies.

2. Description of the Related Art

There exist radio communication systems for providing services of mobilecommunication of a plurality of frequency bands. In such systems, radiocommunication devices, such as mobile terminals, are generally providedwith the same number of transmission signal power amplifiers as that offrequency bands used.

For instance, in the personal digital cellular (PDC) system that usestwo frequency bands, two power amplifiers for the 800-MHz band and1900-MHz band are provided in a single mobile terminal. Even a mobileterminal compatible with different systems, such as an 800-MHz-band PDCand 1900-MHz-band personal handy-phone system (PHS), is provided withpower amplifiers dedicated to respective frequency bands.

In a radio communication device, such as a mobile terminal using aplurality of frequency bands, it is difficult to satisfy a demand forsize reduction if power amplifiers dedicated to the respective frequencybands.

On the other hand, broadband amplifiers for use in measuring devices canamplify signals of different frequency bands. This type of amplifier,however, consumes much power, therefore is not suitable for mobileterminals that use a battery as a power supply. For this reason, theyare not used in mobile terminals.

BRIEF SUMMARY OF THE INVENTION.

It is an object of the invention to provide a power amplifier forselectively amplifying signals of different frequency bands, which canbe made compact, and a radio communication device using the poweramplifier.

According to an aspect of the invention, there is provided a poweramplifier comprising: a first amplifier element configured to amplify afirst input signal of a first frequency, the first amplifier elementincluding a first input terminal which receives the first input signal,and a first output terminal which outputs a first output signal obtainedby amplifying the first input signal; a second amplifier elementconfigured to amplify an input signal of a second frequency, the secondamplifier element including a second input terminal which receives theinput signal of the second frequency, and a second output terminal whichoutputs a signal obtained by amplifying the input signal of the secondfrequency; a power supply input terminal connected to a direct-currentpower supply; a common power supply path including an end connected tothe power supply input terminal, and another end; a first individualpower supply path including an end connected to the another end of thecommon power supply path, and another end connected to the first outputterminal, the first individual power supply path having a firstimpedance; and a second individual power supply path including an endconnected to the another end of the common power supply path, andanother end connected to the second output terminal, the secondindividual power supply path having a second impedance.

According to another aspect of the invention, there is provided a poweramplifier similar to the above but further comprising: a first outputmatching circuit connected to the first output terminal of the firstamplifier element; and a second output matching circuit connected to thesecond output terminal of the second amplifier element.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A is a block diagram of a power amplifier according to a firstembodiment of the invention;

FIG. 1B shows a FET used for each amplifier element in FIG. 1A;

FIG. 1C shows a bipolar transistor used for each amplifier element inFIG. 1A;

FIG. 2 is a diagram useful in explaining the impedance relationshipbetween components in the first embodiment, assumed when an f1 amplifierelement is operating;

FIG. 3 is a diagram useful in explaining the impedance relationshipbetween components in the first embodiment, assumed when an f2 amplifierelement is operating;

FIG. 4 illustrate the configuration of a power amplifier according to asecond embodiment of the invention;

FIG. 5 is a diagram useful in explaining the impedance relationshipbetween components in the second embodiment, assumed when an f3amplifier element is operating;

FIG. 6 shows a first structure example of a power supply circuitincorporated in the first embodiment;

FIG. 7 shows a second structure example of the power supply circuitincorporated in the first embodiment;

FIG. 8 shows a third structure example of the power supply circuitincorporated in the first embodiment;

FIG. 9 shows a fourth structure example of the power supply circuitincorporated in the first embodiment;

FIG. 10 shows a fifth structure example of the power supply circuitincorporated in the first embodiment;

FIGS. 11A and 11B are schematic diagrams illustrating front and backspecific structure examples of the power amplifier of the firstembodiment;

FIGS. 12A, 12B and 12C are schematic diagrams illustrating plural sidespecific structure examples of a power amplifier according to a thirdembodiment;

FIG. 13 is a block diagram of a multi-stage power amplifier according toa fourth embodiment; and

FIG. 14 is a block diagram of a radio communication device according toa fifth embodiment.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

FIG. 1A shows the configuration of a power amplifier according to afirst embodiment-of the invention. The first embodiment will bedescribed using, as an example, a power amplifier operable at twofrequencies f1 and f2.

The power amplifier has input terminals 11 and 12 for receiving inputsignals Vi1 and Vi2 of frequencies f1 and f2. The input signal Vi1 isinput to the input terminal of an f1 amplifier element 17 via an inputmatching circuit 14. The input signal Vi2 is input to the input terminalof an f2 amplifier element 18 via an input matching circuit 15. Thesignal amplified by the amplifier element 17 is output as an outputsignal Vo1 from an output matching circuit 21. Similarly, the signalamplified by the amplifier element 18 is output as an output signal Vo2from an output matching circuit 22.

The amplifier elements 17 and 18 are formed of, for example, the FET asshown in FIG. 1B, or the bipolar transistor as shown in FIG. 1C.Further, each of the amplifier elements 17 and 18 is not always formedof a single transistor, but may be formed of, for example, twotransistors connected in series. In FIG. 1A, reference numerals 1, 2 and3 denote the control electrode and first and second main electrodes ofthe amplifier element 17. If the element 17 is formed of a FET, its gateelectrode G, drain electrode D and source electrode S correspond to thecontrol electrode and first and second main electrodes, respectively.Further, if the element 17 is formed of a bipolar transistor, its baseelectrode B, collector electrode C and emitter electrode E correspondthe control electrode and first and second main electrodes,respectively.

The signals output from the input matching circuits 14 and 15 are inputto the respective control electrodes 1 of the amplifier elements 17 and18. The signals amplified are output from the respective first mainelectrodes 2 of the amplifier elements 17 and 18. The second mainelectrodes 3 of the amplifier elements 17 and 18 are connected to aconstant potential point (not shown), for example, grounded.

The supply of power,. i.e., a DC voltage, to the amplifier elements 17and 18 is performed by a power supply circuit described below. Firstly,one end of a common power supply path 31 is connected to a power supplyinput terminal 30 that is connected to a DC power supply Vcc. The commonpower supply path 31 is connected to both the amplifier elements 17 and18. The other end of the common power supply path 31 is connected to oneend of each of individual power supply paths 32 and 33 dedicated to theamplifier elements 17 and 18, respectively. The other ends of the lines32 and 33 are connected to the respective first main electrodes of theamplifier elements 17 and 18. As described later, the individual powersupply paths 32 and 33 have different impedances.

The operation of the power amplifier of the first embodiment will bedescribed.

The f1 and f2 amplifier elements 17 and 18 operate at differentfrequencies f1 and f2, as described above. However, they are controlledsuch that they operate exclusively. In other words, when one of theelements 17 and 18 is operating, the other is kept inoperative.

The output matching circuit 21 matches impedances with a circuit (notshown) connected after it, when the f1 amplifier element 17 is operatingat the frequency f1. The circuit 21 has a conjugate impedance Z_(P1ON)*with respect to the output impedance Z_(P1ON) of the amplifier element17 during operation. Similarly, the output matching circuit 22 matchesimpedances with a circuit (not shown) connected after it, when the f2amplifier element 19 is operating at the frequency f2. The circuit 22has a conjugate impedance Z_(P2ON)* with respect to the output impedanceZ_(P2ON) of the amplifier element 18 during operation.

The output matching circuits 21 and 22 do not necessarily have conjugateimpedances with respect to the output impedances of the amplifierelements 17 and 18 during operation. They may be adapted to differentpurposes. For instance, the impedances of the output matching circuits21 and 22 may be set so that the output signals Vo1 and Vo2 have themaximum levels and/or the minimum distortion values.

FIG. 2 shows the impedances of the components of FIG. 1A assumed whenthe input signal Vi1 of the frequency f1 is input to the input terminal11, and the f1 amplifier element 17 is operating and the f2 amplifierelement 18 is not operating. The operating amplifier element 17 has theoutput impedance Z_(P1ON). The first main electrode (output terminal) ofthe amplifier element 17 is connected to the output matching circuit 21having the conjugate impedance Z_(P1ON)* with respect to Z_(P1ON), andis also connected to the power supply circuit. The power supply circuithas the common power supply path 31 and individual power supply paths 32and 33, as described above. DC power is supplied to the f1 amplifierelement 17 from the input terminal 30 via the common power supply path31 and individual power supply path 32.

On the other hand, the f2 amplifier element 18, which is not operating,has an output impedance Z4. The impedance Z5 of the output matchingcircuit 22 connected to the first main electrode (output terminal) ofthe amplifier element 18 is identical to the conjugate impedanceZ_(P2ON)* with respect to the output impedance Z_(P2ON) of the amplifierelement 18 during operation.

Assuming that the synthesis impedance when the power supply circuit isviewed from the first main electrode of the operating f1 amplifierelement 17 is Za, Za is given by $\begin{matrix}{Z_{a} = \frac{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)} + Z_{2}}{Z_{2}\left( {Z_{1} + Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)}} & (1)\end{matrix}$where Z1 represents the impedance of the common power supply path 31, Z2and Z3 represent the impedances of the individual power supply paths 32and 33, and Z2≠Z3. The impedances Z1, Z2 and Z3 are expressed as afrequency function, Zn(f)=Rn(f)+Xn(f) (n=1, 2, 3). Rn(f) represents theresistance component, and Xn(f) the reactance component. In equation (1)directed to the case where the input signal Vi1 of the frequency f1 isinput to the input terminal 11, and the f1 amplifier element 17 isoperating, Z1, Z2 and Z3 are Z1(f1), Z2 (f1) and Z3 (f1), respectively.

At this time, if the real part Re{Za} of the synthesis impedance Za isset higher than the real part Re{Z_(P1ON) 8} of the impedance Z_(P1ON)*of the output matching circuit 21, as shown in the following formula(2), the output signal (high frequency power) of the amplifier element17 is efficiently guided to the output side via the output matchingcircuit 21, and output as the output signal Vo1.Re{Z _(a) }>Re{Z _(P1ON)*}  (2)

The greater the difference between Re{Za} and Re{Z_(P1ON) 8}, the higherthe effect. If Re{Za} is five times or more Re{Z_(P1ON) 8}, and morepreferably if the former is ten times or more the latter, the greaterpart of the high-frequency power of the output signal of the f1amplifier element 17 can be output as the output signal Vo1.

FIG. 3 shows the impedances of the components of FIG. 1A assumed whenthe input signal Vi2 of the frequency f2 is input to the input terminal12, and the f2 amplifier element 18 is operating and the f1 amplifierelement 17 is not operating. The operating amplifier element 18 has theoutput impedance Z_(P2ON). The first main electrode (output terminal) ofthe amplifier element 18 is connected to the output matching circuit 22having the conjugate impedance Z_(P2ON)* with respect to Z_(P2ON), andis also connected to the power supply circuit. In the power supplycircuit, DC power is supplied to the f2 amplifier element 18 from theinput terminal 30 via the common power supply path 31 and individualpower supply path 33.

On the other hand, the f1 amplifier element 17, which is not operating,has an output impedance Z6. The impedance Z7 of the output matchingcircuit 21 connected to the first main electrode (output terminal) ofthe amplifier element 17 is identical to the conjugate impedanceZ_(P1ON)* with respect to the output impedance Z_(P1ON) of the amplifierelement 17 during operation.

Assuming that the synthesis impedance when the power supply circuit isviewed from the first main electrode of the operating f2 amplifierelement 18 is Zb, Zb is given by $\begin{matrix}{Z_{b} = \frac{{Z_{1}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)} + Z_{3}}{Z_{3}\left( {Z_{1} + Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}} & (3)\end{matrix}$

In equation (3) directed to the case where the input signal Vi2 of thefrequency f2 is input to the input terminal 12, and the f2 amplifierelement 18 is operating, Z1, Z2 and Z3 in the equation (3) are Z1(f2),Z2 (f2) and Z3 (f2), respectively.

At this time, if the real part Re{Zb} of the synthesis impedance Zb isset higher than the real part Re{Z_(P2ON)*} of the impedance Z_(P2ON)*of the output matching circuit 22, as shown in the following formula(4), the output signal (high frequency power) of the amplifier element18 is efficiently guided to the output side via the output matchingcircuit 22, and output as the output signal Vo2.Re{Z _(b) }>Re{Z _(P2ON)*}  (4)

Also in this case, if Re{Zb} is five times or more Re{Z_(P2ON)*}, andmore preferably if the former is ten times or more the latter, thegreater part of the high-frequency power of the output signal of the f2amplifier element 18 can be output as the output signal Vo2.

From the above formulas (1) to (4), Z1, Z2 and Z3 are determined.

As described above, the power supply circuit for supplying power to theamplifier elements 17 and 18 comprises the common power supply path 31commonly provided for the amplifier elements 17 and 18, and theindividual power supply paths 32 and 33 provided for the amplifierelements 17 and 18, respectively, and having different impedances. Byvirtue of this structure, the power amplifier can be made compact.

The advantage of the above structure will now be described. Assume thatthe area of the common power supply path 31 is S1, and those of theindividual power supply paths 32 and 33 are S2 and S3, respectively. Ina power amplifier having a single amplifier element operable at a singlefrequency, the power supply circuit needs an area of (S1+S2) or (S1+S3)(i.e., the sum of the area S1 of the common power supply path and one ofthe areas S2 and S3 of the individual power supply paths). Accordingly,where two individual power supply circuits are provided for twoamplifier elements, an area of (2S1+S2+S3) is needed.

On the other hand, the area of the power supply circuit employed in theembodiment is (S1+S2+S3), which is smaller by S1 than the case whereindividual power supply circuits are provided for two amplifierelements. Since, in general, the power supply circuit occupies arelatively large area in the power amplifier, reduction of the area ofthe power supply circuit significantly contributes to the reduction ofthe size of the power amplifier.

In the embodiment, the output matching circuits 21 and 22 are set tohave conjugate impedances with respect to the output impedances of theamplifier elements 17 and 18 during operation, respectively. However,the impedances of the circuits 21 and 22 are not limited to theconjugate ones, but may be varied in accordance with purposes.

Second Embodiment

The power amplifier of the first embodiment is operable at twofrequencies f1 and f2. However, a power amplifier that is operable atthree or more frequencies can be realized. In this case, it issufficient if the power amplifier comprises three or more amplifierelements, a single common power supply path, three or more individualpower supply paths and three or more output matching circuits. FIG. 4shows a power amplifier according to a second embodiment, which isoperable at three frequencies f1, f2 and f3. In FIGS. 4 and 5, elementssimilar to those in FIG. 1A are denoted by corresponding referencenumerals.

The second embodiment employs a f3 amplifier element 19, as well as thef1 and f2 amplifier elements 17 and 18. DC power input to the powersupply input terminal is supplied to one end of the common power supplypath 31. After that, the DC power is distributed to the f1 amplifierelement 17 via the individual power supply path 32, to the f2 amplifierelement 18 via the individual power supply path 33, and to the f3amplifier element 19 via the individual power supply path 34. Theindividual power supply paths 32, 33 and 34 have different impedances,as will be described later.

FIG. 5 shows the impedances of the components of FIG. 4 assumed when aninput signal Vi3 of a frequency f3 is input to an input terminal 13, andthe f1 and f2 amplifier elements 17 and 18 are not operating and the f3amplifier element 19 is operating. The operating amplifier element 19has an output impedance Z_(P3ON). The first main electrode (outputterminal) of the amplifier element 19 is connected to an-output matchingcircuit 23 having a conjugate impedance Z_(P3ON)* with respect toZ_(P3ON), and is also connected to the power supply circuit.

On the other hand, the f1 amplifier element 17, which is not operating,has an output impedance Z6. The impedance Z7 of the output matchingcircuit 21 connected to the first main electrode (output terminal) ofthe amplifier element 17 is identical to the conjugate impedanceZ_(P1ON)* with respect to the output impedance Z_(P1ON) of the amplifierelement 17 during operation. Similarly, the f2 amplifier element 18,which is not operating, has an output impedance Z4. The impedance Z5 ofthe output matching circuit 22 connected to the first main electrode(output terminal) of the amplifier element 18 is identical to theconjugate impedance Z_(P2ON)* with respect to the output impedanceZ_(P2ON) of the amplifier element 18 during operation.

Assuming that the synthesis impedance when the power supply circuit isviewed from the first main electrode of the operating f3 amplifierelement 19 is Zc, Zc is given by $\begin{matrix}{Z_{c} = {Z_{8} + \frac{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}{\begin{matrix}{{\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)} +} \\{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)} + {Z_{1}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}}\end{matrix}}}} & (5)\end{matrix}$

In equation (5) directed to the case where the input signal Vi3 of thefrequency f3 is input to the input terminal 13, and the f3 amplifierelement 19 is operating, Z1, Z2 and Z3 are Z1(f3), Z2 (f3) and Z3 (f3),respectively.

Similarly, the synthesis impedance Za, obtained if the power supplycircuit is viewed from the first main electrode of the f1 amplifierelement 17 when the element 17 is operating and the elements 18 and 19are not operating, is given by the following equation (6). The synthesisimpedance Zb, obtained if the power supply circuit is viewed from thefirst main electrode of the f2 amplifier element 18 when the element 18is operating and the elements 17 and 19 are not operating, is given bythe following equation (7). $\begin{matrix}{Z_{a} = {Z_{2} + \frac{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}{\begin{matrix}{{\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)} +} \\{{Z_{1}\left( {Z_{3} + \frac{Z_{4}Z_{5}}{Z_{4} + Z_{5}}} \right)} + {Z_{1}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}}\end{matrix}}}} & (6) \\{Z_{b} = {Z_{3} + \frac{{Z_{1}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}{\begin{matrix}{{\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)} +} \\{{Z_{1}\left( {Z_{2} + \frac{Z_{6}Z_{7}}{Z_{6} + Z_{7}}} \right)} + {Z_{1}\left( {Z_{8} + \frac{Z_{9}Z_{10}}{Z_{9} + Z_{10}}} \right)}}\end{matrix}}}} & (7)\end{matrix}$

In equation (6) directed to the case where the input signal Vi1 of thefrequency f1 is input to the input terminal 11, and the f1 amplifierelement 17 is operating, Z1, Z2 and Z3 are Z1(f1), Z2 (f1) and Z3 (f1),respectively. Similarly, in equation (7) directed to the case where theinput signal Vi2 of the frequency f2 is input to the input terminal 12,and the f2 amplifier element 18 is operating, Z1, Z2 and Z3 are Z1(f2),Z2 (f2) and Z3 (f2), respectively.

In those cases, if the real parts Re{Za}, Re{Zb} and Re{Zc} of thesynthesis impedances Za, Zb and Zc are set higher than the real partsRe{Z_(P1ON) 8}, Re{Z_(P2ON)*} and Re{Z_(P3ON)*} of the impedancesZ_(P1ON)* , Z_(P2ON)* and Z_(P3ON)* of the output matching circuits 21,22 and 23, respectively, as shown in the following formulas (8), (9) and(10), the output signals (high frequency power) of the amplifierelements 17, 18 and 19 are efficiently guided to the output side via theoutput matching circuits 21, 22 and 23, and output as the output signalsVo1, Vo2 and Vo3, respectively.Re{Z _(a) }>Re{Z _(P1ON)*}  (8)Re{Z _(b) }>Re{Z _(P2ON)*}  (9)Re{Z _(c) }>Re{Z _(P3ON)*}  (10)

From the formulas (1) to (10), Z1, Z2 and Z3 are determined. Even in thecase of a power amplifier including four or more amplifier elements, theimpedances of the common power supply path and individual power supplypaths can be determined by executing the same procedure as the above.

Moreover, as in the first embodiment, if the real parts Re{Za}, Re(Zb)and Re(Zc) of the synthesis impedances Za, Zb and Zc are five times ormore Re{Z_(P1ON)*}, Re{Z_(P3ON)*} and Re{Z_(P2ON)*}, respectively, andmore preferably if the formers are ten times or more the latters, thegreater part of the high-frequency power of the output signals of thef1, f2 and f3 amplifier elements 17, 18 and 19 can be output as theoutput signals Vo1, Vo2 and Vo3.

A description will be given of more specific power amplifier examplesaccording to the first and second embodiments.

FIG. 6 shows a first example of the power amplifier of the firstembodiment that is operable at the frequencies f1 and f2. In thisexample, the power supply circuit is formed of a plurality of spiralinductors. A spiral inductor 41 corresponds to the common power supplypath 31, and spiral inductors 42 and 43 correspond to the individualpower supply paths 32 and 33, respectively. The impedances of the spiralinductors 41, 42 and 43 are given byZ ₁ =R ₁ +jωX ₁   (11)Z ₂ =R ₂ +jωX ₂   (12)Z ₃ =R ₃ +jωX ₃   (13)where R1, R2 and R3 represent the resistance components, and X1, X2 andX3 the reactance components. R1, R2, R3, X1, X2 and X3 can be determinedby combining the equations (11), (12) and (13) with the formulas (1),(2), (3) and (4), and setting an appropriate frequency.

FIG. 7 shows a second example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed ofmeander lines and capacitors. A meander line 51 corresponds to thecommon power supply path 31, and meander lines 52 and 53 correspond tothe individual power supply paths 32 and 33, respectively. Capacitors54, 55 and 56 are provided between the input terminals of the meanderlines 51, 52 and 53 and the earth, respectively.

FIG. 8 shows a third example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed oftransmission lines and bonding wires. A straight transmission line 61A,T-shaped transmission line 61B and boding wire 64 connecting themprovide a common power supply path corresponding to the common powersupply path 31 in FIG. 1A. The T-shaped transmission line 61B,transmission line 62 and boding wire 65 connecting them provide anindividual power supply path corresponding to the individual powersupply path 32 in FIG. 1A. Similarly, the T-shaped transmission line61B, transmission line 63 and boding wire 66 connecting them provide anindividual power supply path corresponding to the individual powersupply path 33 in FIG. 1A. Desired impedances can be obtained bychanging the lengths and/or thicknesses of the bonding wires 64, 65 and66.

FIG. 9 shows a fourth example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed of chipcomponents that include capacitors and inductors. A capacitor 71 andinductor 72 provide a common power supply path corresponding to thecommon power supply path 31 in FIG. 1A. A capacitor 73 and inductor 74provide an individual power supply path corresponding to the individualpower supply path 32 in FIG. 1A, while a capacitor 75 and inductor 76provide an individual power supply path corresponding to the individualpower supply path 33 in FIG. 1A.

FIG. 10 shows a fifth example of the power amplifier of the firstembodiment. In this example, the power supply circuit is formed ofinductors or median lines using via holes. Specifically, wiring layers81 and 82 on the upper and lower surfaces of a plate 80 called a moduleplate, respectively. Each of the wiring layers 81 and 82 has atransmission line 83 of a predetermined pattern. The upper and lowersurfaces of the substrate 80 are connected to each other by via holes84, thereby forming inductors or median lines.

Also in the second to fifth examples, R1, R2, R3, X1, X2 and X3 can bedetermined by combining the equations (11), (12) and (13) with theformulas (1), (2), (3) and (4), and setting an appropriate frequency.

FIGS. 11A and 11B shows front and back structures of a sixth example ofthe power amplifier of the first embodiment, respectively. In thisexample, the amplifier elements and power supply circuit are provided ondifferent layers of a multilayer substrate. Specifically, the f1 and f2amplifier elements 17 and 18 and individual power supply paths 32 and 33are provided on the upper surface of a multilayer substrate 90, whilethe common power supply path 31 is provided on the lower surface of thesubstrate 90.

Third Embodiment

FIGS. 12A , 12B and 12C show, respectively, plural structures of a poweramplifier according to a third embodiment that is operable at the fourfrequencies f1, f2, f3 and f4. This power amplifier employs thestructure shown in FIG. 11A and 11B. Specifically, f1 and f2 amplifierelements 17 and 18 and individual power supply paths 22 and 23 areprovided on the upper surface 91 of a multilayer substrate. A commonpower supply path 21 is provided on the intermediate layer 92 of thesubstrate. Further, f3 and f4 amplifier elements 19 and 20 andindividual power supply paths 24 and 25 are provided on the lowersurface 93 of the substrate.

Fourth Embodiment

FIG. 13 shows a power amplifier according to a fourth embodiment of theinvention. The power amplifiers of the first and second embodiments havea single-stage structure, while the power amplifier of the fourthembodiment has a dual-stage structure.

In the fourth embodiment, input signals Vi1 and Vi2 of frequencies f1and f2, supplied to input terminals 11 and 12, are input to thefirst-stage f1 and f2 amplifier elements 17A and 18 via input matchingcircuits 14 and 15, respectively. The outputs of the first-stage f1 andf2 amplifier elements 17A and 18A are input to the second-stage f1 andf2 amplifier elements 17B and 18B via intermediate matching circuits 24and 25, respectively. The outputs of the second-stage f1 and f2amplifier elements 17B and 18B are extracted as output signals Vo1 andVo2 via output matching circuits 21 and 22, respectively.

DC power is supplied to the first-stage f1 and f2 amplifier elements 17Aand 18A via a first power supply circuit that has a common power supplypath 31 A and individual power supply paths 32A and 33A. Similarly, DCpower is supplied to the second-stage f1 and f2 amplifier elements 17Band 18B via a second power supply circuit that has a common power supplypath 31B and individual power supply paths 32B and 33B. The fourthembodiment can be modified into a power amplifier including athree-stage or more structure.

Fifth Embodiment

A description will be given of a radio communication device according toa fifth embodiment of the invention, in which the power amplifier of thefirst embodiment is incorporated in the transmission system of thedevice. FIG. 14 shows the configuration of a radio communication deviceoperable at two frequency bands.

Firstly, the receiving system of the device will be described. An RFreception signal received by an antenna 100 is guided to the receivingsystem via a duplexer 101, and distributed into two receiving routes bya switch 102 in accordance with its frequency. If the RF signal isdistributed into a first receiving route, it is guided to a mixer 107via a band-pass filter (CPF) 103 and low noise amplifier (LNA) 105, andis subjected to frequency conversion based on a local signal from alocal signal source 109, i.e., it is down-converted.

The output signal of the mixer 107 is simultaneously input to two mixers112 and 113 via a band-pass filter 110. The mixers 112 and 113 providean orthogonal demodulator, receive orthogonal local signals from a localsignal source 114, and convert the signals, supplied from the band-passfilter 110, into orthogonal reception baseband signals, i.e., I and Qsignals. The orthogonal reception baseband signals are input to abaseband processing unit 120, where they are reproduced as receiveddata.

A second receiving route is similar to the first one, and comprises aband-pass filter 104, low noise amplifier 106, mixer 108, band-passfilter 108, mixers 115 and 116, and local signal source 117. The localsignal source 117 generates local signals of a frequency different fromthat of the local signals generated by the local signal source 114.

The transmission system will now be described. The baseband processingunit 120 performs digital signal processing on transmission data,thereby generating orthogonal transmission baseband signals, i.e., I andQ signals. The generated I/Q signals are input to one of thetransmission routes in accordance with their transmission frequency. Ifthe I/Q signals are input to a first transmission route, they aremultiplied, in mixers 121 and 122, by the respective orthogonal localsignals from a local signal source 123. The output signals of the mixers121 and 122 are added by an adder 127. The mixers 121 and 122 and adder127 form an orthogonal modulator.

The output signal of the adder 127 is guided to a mixer 129, where it issubjected to frequency conversion based on a local signal from a localsignal line 131, i.e., it is up-converted. The output signal of themixer 129 is supplied to a band-pass filter 132, where an unnecessarycomponent is eliminated therefrom. After that, the resultant signal isamplified by a power amplifier 134. The output signal of the poweramplifier 134 is guided to a switch 137 via a low-pass filter 135, andthen to the antenna 100 via the duplexer 101. Thus, the signal is outputas an electric wave from the antenna.

The other transmission route, i.e., a second route, is similar to thefirst one, and comprises mixers 124 and 125 and adder 128 providing anorthogonal modulator, local signal source 126 for the orthogonalmodulator, mixers 129 and 130 and local signal line 131 forup-conversion, band-pass filter 133, power amplifier 134 and low-passfilter 136. The transmission frequency, i.e., the frequency of atransmission signal input to the power amplifier 134, differs from thatof the first transmission route.

If the power amplifier of the first embodiment is used as the poweramplifier 134, it can be commonly used for two transmission routes. Thisbeing so, the whole area required for the power amplifier can be reducedcompared to the case where respective power amplifiers are used for twotransmission routes, which contributes to the reduction of the size andcost of the radio communication device. Further, a radio communicationdevice having three or more frequencies can be realized by modifying theconfiguration of FIG. 14.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1-16. (canceled)
 17. A power amplifier comprising: a first amplifierelement configured to amplify a first input signal of a first frequency,the first amplifier element including a first input terminal whichreceives the first input signal, and a first output terminal whichoutputs a first output signal obtained by amplifying the first inputsignal; a second amplifier element configured to amplify a second inputsignal of a second frequency, the second amplifier element including asecond input terminal which receives the second input signal, and asecond output terminal which outputs a signal obtained by amplifying thesecond input signal; a power supply input terminal connected to adirect-current power supply; a common power supply path including an endconnected to the power supply input terminal, and another end; a firstindividual power supply path including an end connected to the anotherend of the common power supply path, and another end connected to thefirst output terminal, the first individual power supply path having afirst impedance; a second individual power supply path including an endconnected to the another end of the common power supply path, andanother end connected to the second output terminal, the secondindividual power supply path having a second impedance; a first outputmatching circuit connected to the first output terminal of the firstamplifier element; and a second output matching circuit connected to thesecond output terminal of the second amplifier element, wherein: a firstamplifier element and the second amplifier element are controlledexclusively to operate the first amplifier element and the secondamplifier element; and the common power supply path, the firstindividual power supply path and the second individual power supplypath, the first output matching circuit and second output matchingcircuit have respective impedances, each of the respective impedancesbeing set to a value so that a real part of a synthesis impedance viewedfrom one selected from the first amplifier element and second amplifierelement that is in operation, to a corresponding one selected from thefirst and second individual power supply paths, is greater than a realpart of a corresponding one selected from the first output matchingcircuit and second output matching circuit.
 18. A radio communicationdevice which performs data reception and transmission using onefrequency band selected from a plurality of frequency bands, comprising:a transmission signal generator which generates a transmission signal ofthe one frequency band; and the power amplifier according to claim 17,the power amplifier receiving the transmission signal as an inputsignal.